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where im at in cali I cant remember ever seeing a system that wasnt done by a 500sqft rule, at best its a half ton under the rule. at some point I plan to get into heat load calcs, to many bad practices here.

where im at in cali I cant remember ever seeing a system that wasnt done by a 500sqft rule, at best its a half ton under the rule. at some point I plan to get into heat load calcs, to many bad practices here.

I would suggest investing in a good load cal program like wrightsoft and learn the ways of how to size a home hvac system properly. Takes the guess work out as long as used propely.

Plus can be a lifesaver when customer says my existing system just want cool my home. You can then preform a Load cal and see what the home needs if load shows you there current system is sized propely or even oversized but still want cool you have taken the system out of the equation. Then you have to start looking at ductwork (manual d). It's amazing what a little hardwork with the right software can yield for customers home.

To many times in my area customer says my home not cooling right. Other contractors come in and say will upsize it by a 1/2 ton of ton and that will fix that? What they fail to do is see if the ductwork can handle the extra size equipment and install a bigger system on a already undersized ductwork.

just cruising through the wrightsoft site doesnt seem like it is to hard to do, how long does it take you to pull heat load calc after youve done a few, say single floor home, 3 beds, 2 baths, living room, kitchen, laundry room, 1800sqft? also is that app downloadable or does it need internet?

Los Angeles 2.5% summer design is 89F & 70F wet bulb; so let's not oversize the A/C.
Reducing the required size of the A/C will help make the duct system problems easier & less costly to resolve.

Before doing anything else, I'd have a Home Energy Efficiency Audit performed; the Power Company may have a program.
After the retro-work is done, do a heat gain/loss load-calc & size-down as much as possible.

The oversized A/C is creating a lot of costly problems that would be somewhat ameliorated if it can be sized-down enough....

A 3" vent on the 50 gallon water heater? The 4.25 inches you're stating for the flue must be a 5" (I've never seen odd numbers on a flue) and at 20+ feet it'll carry 155,000 btus. What size is the furnace?

Jacob-k is correct...........the 30"x10" return is not large enough. I don't care that every home is the same or that it has "worked" all these years. It is killing the efficiency and output of the equipment. Also, I still can not believe that a 4 ton is what the home needs. Unless it is extremely hot in Irvin, CA. and the homes have no insulation, poor windows and no attic ventilation. I A/C a 2,250 sq. ft 2-story with a 2.5 ton as an example. I'm sure our humidity is higher.

Yes, you're right, I just went and measured the water heater vent, it's 3 inch (not 2.5 I stated earlier).
That flue is 5" on OD, but 4.25 ID (3/8 wall thk). Thanks for the 155,000 BTU number, it helps me to get a sense of what capability is in place. The current 33 yr old furnace has a 60,000 BTU rating, so combining the 40,000 BTU water heater with it thru that 5" pipe looks like workable combination.

I would be very surprised and extremely impressed with the engineer that made a 10x30 return on a 4 ton system operate at .5 TESP...

The man said it worked for 33 years. He didn't say it was efficient or quiet. A 10 x 30 duct can handle 1600 cfm at .062 inch per 100 ft of ESP. So if it's going 10 feet or 3x that, 30 ft, for fittings that's .0185". The register at 1600 CFM using 3/4" blade spacing at 0 deg def could be around .111 ESP at that size at an NC of about 35 (personally I don't like to go over 20 NC, but 35 is not exorbitant); a bit high but acceptable. So far we're at .0185" + .111" = .1295" that leaves .3705" for supply at .5" ESP. I think that can be done.

My home seems to be well insulated; I see it in attic and exterior walls. Also have double paned windows. Our climate here is mild I only use the A/C about 6 weeks per year in Aug and Sept when temps get to max of 100 F outside, even then the nights always cool down below 85 F. We use the furnace much more frequently maybe 5 months per year, but outside temps rarely get below 30 F.

So is it fairly certain that I would be better off with a 3 ton system for my home? If George2 gets 2.5 tons to work adequately in homes that are 10% bigger than mine in climates that are more extreme that almost seems proof enough that 3 tons would work for me. And as udarrell stated that should make the current vent and return opening issues less severe?

My home seems to be well insulated; I see it in attic and exterior walls. Also have double paned windows. Our climate here is mild I only use the A/C about 6 weeks per year in Aug and Sept when temps get to max of 100 F outside, even then the nights always cool down below 85 F. We use the furnace much more frequently maybe 5 months per year, but outside temps rarely get below 30 F.

So is it fairly certain that I would be better off with a 3 ton system for my home? If George2 gets 2.5 tons to work adequately in homes that are 10% bigger than mine in climates that are more extreme that almost seems proof enough that 3 tons would work for me. And as udarrell stated that should make the current vent and return opening issues less severe?

How many supply registers does your home have on the second floor and how many registers on the first floor? Where are the registers on each floor located? Thanks......that will help determine the airflow. Can you control the airflow other than at the register itself?

Is there a forced power vent on the water heater and the furnace? Power venting increases the capacity allowed through the vent. Also the vent material makes a difference. Since it was used in multiple houses in a tract setting, chances are it was an engineered design calculated to show the code official that it would work. The code allows that option. Apparently it does work for the system that was installed. 33 years is decent life expectancy for that type equipment. Same goes for the return air. As long as the total external static pressure at design CFM of the fan is not exceeded, the return opening can be small. And again, that is probably the case because of the tract situation. The design was probably engineered, calculated and shown to work so it could be used multiple times to save first cost money, with little thought to energy savings. Not to say that larger or more openings wouldn't work better especially in the case of the RA grille.

No forced air on the vent, just a mostly vertical run of 5" (4.25 ID) pipe.
The return register is on a wall in my family room about 2 ft away from the furnace that is behind that wall in the garage.

How many supply registers does your home have on the second floor and how many registers on the first floor? Where are the registers on each floor located? Thanks......that will help determine the airflow. Can you control the airflow other than at the register itself?

Only that one 30 x 10 register on the bottom floor. All the air pulled by the fan has to pass thru it (and tiny cracks that ants like to crawl thru )

How's the noise level when the system is running? Do you hear air noise (hiss) from the register? Everyone saying that it should be noisy at correct CFM for 4 tons are right. It would run about 35 NC through that register, which is at the high level of acceptability of the design standards for residential. A larger one would likely run quieter, all else being the same.

Yes, it's kind of noisy, my command central station (Lazy-Boy recliner) is right next to it and my finely tuned reflexes quickly hit the Volume up button on the remote when the fan kicks on. The register actually makes a humming sound.

Yes, it's kind of noisy, my command central station (Lazy-Boy recliner) is right next to it and my finely tuned reflexes quickly hit the Volume up button on the remote when the fan kicks on. The register actually makes a humming sound.

Since the unit is so close, that could be machine noise from the unit. Reducing the unit to better match the load could improve that. Making a larger opening might not, so holding off on that is not a bad thought.